The present invention generally relates to lasers, and more particularly is concerned with fiber optic semiconductor ring lasers.
In recent years, the aviation industry has been involved in a seemingly never ending quest to enhance the performance of modern avionics. One particular area in which avionics engineers have expended much effort and achieved many successes, is in the substitution of completely electro-optical systems for the conventional mechanical systems of the past. A prime example of these efforts is in the area of inertial navigation systems.
Mechanical gyroscopes have been, for years, a central component to any inertial navigation system. Recently, the helium neon (He-Ne) ring laser gyroscope has replaced many of the mechanical gyros. However, these He-Ne ring laser gyros have disadvantages in cost and size, among others. With the recent advent of the global positioning system, which uses satellite communications to assist inertial navigation systems, the fiber optic ring laser gyroscopes are becoming more attractive.
Numerous ring lasers which incorporate optical fibers have been used in the past for several applications. One example of a ring laser which uses a fiber optic resonant ring is described in U.S. Pat. No. 4,405,236, entitled "Semiconductor Ring Laser Apparatus", which was issued on Sept. 20, 1983 to Mitsuhashi et al., which patent is incorporated herein by this reference.
While the Mitsuhashi apparatus is capable of producing a ring laser, it does have several disadvantages. A major problem with this approach is that it has a reduction in internal diode reflections, but only at the cost of the overall performance of the laser. The Mitsuhashi design utilizes a diode with its waveguide region being oriented at Brewster's Angle with respect to the normal to the diode cleavage plane. Also at this angle with respect to the cleavage plane is each end of the fiber optic ring. The use of Brewster's Angle was intended to reduce the reflections from within the diode and thereby allowing for the fiber ring to act as the resonant cavity. However, when Brewster's Angle is used, the overall power of the laser is often less than optimal.
Consequently, a need exists for the improvement in fiber optic ring lasers which reduce internal diode reflections, while still providing a high degree of power out of the ring laser.